p5js sketch file with a nice color palette.

palette-sketch.js

function setup() {
  createCanvas(800, 800, WEBGL);
}

function draw() {

  background("#fefefe");

  let scaleFactor = 1;

  // black - red - orange
  let colors1 = [
    "03071e",
    "370617",
    "6a040f",
    "9d0208",
    "d00000",
    "dc2f02",
    "e85d04",
    "f48c06",
    "faa307",
    "ffba08"
  ];

  // white - dark gray
  let colorsGray = [
    "f8f9fa",
    "e9ecef",
    "dee2e6",
    "ced4da",
    "adb5bd",
    "6c757d",
    "495057",
    "343a40",
    "212529"
  ];

  // bluish/green - orange
  let c = [
    "16697a",
    "489fb5",
    "82c0cc",
    "ede7e3",
    "ffa62b"
  ];

  // yellow, orange, magenta, violet blue
  let c3 = [
    "ffbe0b",
    "fb5607",
    "ff006e",
    "8338ec",
    "3a86ff"
  ];
  
  // magenta - violet - light blue
  let c4 = [
    "f72585",
    "b5179e",
    "7209b7",
    "560bad",
    "480ca8",
    "3a0ca3",
    "3f37c9",
    "4361ee",
    "4895ef",
    "4cc9f0"
  ];

  // red - orange - green - blue
  let c5 = [
    "f94144",
    "f3722c",
    "f8961e",
    "f9844a",
    "f9c74f",
    "90be6d",
    "43aa8b",
    "4d908e",
    "577590",
    "277da1"
  ];

  // red, yellow, green, blue and violet
  let c6 = [
    "ff595e",
    "ffca3a",
    "8ac926",
    "1982c4",
    "6a4c93"
  ];

  // bluish grayscale from dark to light
  let c7 = [
    "0d1b2a",
    "1b263b",
    "415a77",
    "778da9",
    "e0e1dd"
  ];

  strokeWeight(2);
  scale(scaleFactor);

  palets = [
    colors1,
    colorsGray,
    c,
    c3,
    c4,
    c5,
    c6,
    c7
  ];

  // draw palette
  for(k = 0; k < palets.length; k++) {
    for(j = 0; j < palets[k].length; j++) {
      let cp = palets[k].map(function(i) { return '#' + i; });
      fill(cp[j]);
      stroke(cp[j]);
      square((j+1)*30 - 200, 2*k*20 - 200, 20);
    }
  }
}

This is a screenshot of the generated code: